e15060 Background: In metastatic Breast Cancer (mBC) Circulating Tumor Cells (CTCs) are an established prognostic indicator of patients (pts) with highly aggressive disease, poor clinical outcomes, and poor response rates to therapy. However, CTCs are typically found in 90% of mBC, and are indicators of poor clinical outcomes independent of CTCs. We conducted a prospective study to model CTC TNBC (44%), ER/PR+ (30%), HER2+ (15%). Pts were treated with chemotherapy alone (18%), immune checkpoint inhibitor (46%), targeted (40%), hormone (8%) and unknown (5%). 38% (81/212) pts had ≥1 CTCs which correlated with significantly poorer PFS (HR = 1.9; 95%CI 1.3-2.7; p = 0.0016) and OS (HR = 2.0; 95%CI, 1.3-3.0; p = 00025), with the most significant risk at ≥8 CTCs (14% pts), PFS (HR = 3.8; 95%CI, 2.1-6.9; p 40um size (84% pts) had significantly poorer PFS (HR = 2.0; 95% CI, 1.2-3.1; p = 0.0032), but not OS (HR = 1.5; 95%CI, 0.9-2.7; p = 0.1169). However, a threshold of >125um size CAML (43% pts) also had significantly poorer PFS (HR = 1.8; 95% CI, 1.2-2.7; p = 0.0013) and OS (HR = 1.6; 95% CI, 1.0-2.5; p = 0.0233). By combining models, the best outcomes were seen in pts with 0 CTCs & 0 CAMLs (mPFS = 12.6 & mOS = 21.3), followed by 0 CTCs & ≥40um CAMLs (mPFS = 5.2 & mOS = 17.5) and 0 CTCs & ≥125um CAMLs (mPFS = 4.9 & mOS = 15.2). Poorer outcomes were seen with ≥1 CTCs (mPFS = 3.3 & mOS = 13.5) and the worst outcomes with ≥8 CTCs (mPFS = 2.5 & mOS = 4.8). Conclusions: CTCs were uncommon in mBC pts but correlated with very poor clinical outcomes. In parallel analysis, CAMLs were common with CAML size correlating with increasingly poorer outcomes. By combining CTC & CAML subtypes, mBC pts were more accurately stratified by risk of progression and death. Additional multivariate studies correlating treatment class and tumor response rates are ongoing.
Ali et al. (Thu,) studied this question.